Osteoarthritis (OA) is a group of overlapping distinct diseases, which may have different etiologies but similar biologic, morphologic, and clinical outcomes. The disease process not only affects the articular cartilage, but involves the entire joint, including the subchondral bone, ligaments, capsule, synovial membrane, and periarticular muscles. Ultimately, the articular cartilage degenerates with fibrillation, fissures, ulceration, and full thickness loss of the joint surface. This condition is characterised by focal areas of loss of articular cartilage within synovial joints, associated with hypertrophy of bone (osteophytes and subchondral bone sclerosis) and thickening of the capsule. It may be interpreted as the reaction of synovial joints to injury. This phenomenon can occur in any joint, but is most common in selected joints of the hand, spine, knee, foot and hip. This pathological change, when severe, results in radiological changes (loss of joint space and osteophytes), which have been used in epidemiological studies to estimate the prevalence of OA at different joint sites. The molecular and cellular mechanisms at the basis of the onset of OA are, at present, unknown; it is hypothesised that abnormal load as well as trauma may have a role, but it seems certain that genetics and heritable factors are also involved. Inflammation, when present, is only secondary to a primary event.
OA is the most common form of arthritis. The World Health Organization (WHO) estimates that, worldwide, 9.6% of men and 18% of women aged over 60 years have symptomatic OA, classifying OA as the 4th cause of disability in women and the 8th cause in men. It is considered that the risk of disability is the same for knee OA as for cardiac disease.
Rheumatoid arthritis (RA), another common form of arthritis, is a chronic inflammatory disease characterized by articular synovitis leading to cartilage degradation, bone erosion and pain, leading to severe disability and premature mortality.
Though OA and RA can be triggered by different causes and progress according to different pathways, they share the underlying process which consists of an imbalance in cartilage matrix synthesis and breakdown, leading to the destruction of the articular cartilage which in turn results in restricted joint movement, joint instability, pain and chronic disability. Moreover, in spite of the impressive number of patients affected by OA and RA, relatively little is known regarding their aetiology, pathogenesis, and progression. Even more impressively, very few, disease-modifying agents antirheumatic drugs (DMARD) exist for their treatment, and they are mainly limited to RA.
For OA, in the absence of a cure, treatment can only be palliative, being limited to the use of COX-2 selective inhibitors, such as celecoxib, and traditional non-steroidal anti-inflammatory drugs (NSAIDs), such as naproxen and diclofenac, or even older drugs for pain control, such as acetaminophen. An additional class of drugs, which includes compounds such as chondroitin and glucosamine sulfate, also exists as a treatment option for OA, but many physicians remain unconvinced about their efficacy.
Concerning RA, over the last decade, the optimal use of DMARDs, in particular methotrexate and the availability of new biologic agents, typically supported by NSAIDs and/or corticosteroids to provide pain relief, as well as to control inflammation to some degree have dramatically enhanced the success of its management. However, traditional DMARDs have a slow onset of action and toxicity that mandates frequent monitoring. Moreover, NSAIDs use has been overshadowed by gastrointestinal side-effects, when considering classical NSAIDs drugs, and by cardiovascular and renal side-effects when considering selective COX-2 inhibitors.
Therefore, the research for new therapeutic agents preventing cartilage degradation is of great interest, since OA and RA affect millions of people all over the world with an expected incidence rising with the increase of the average population age.
The degradation of cartilage occurring in OA and RA is the result of enzymatic cleavage of its structural components. Cartilage is mainly constituted by chondrocytes and an extracellular matrix (ECM) that consists of proteoglycans (mainly aggrecan), collagens and water. Within the matrix, the interaction between aggrecan, hyaluronic acid (HA) and Type II collagen provides the cartilage with unique compressibility and elasticity, biomechanical properties for weight bearing and joint motion functions. Aggrecan consists of three globular regions: G1 and G2 near the N-terminus of the protein and G3 at the C-terminus. The G1 and G2 regions are separated by a short interglobular domain (IGD) while the G2 and G3 regions are separated by a long glycosaminoglycan (GAG) attachment region. The G1 domain constitutes, through an ancillary protein, the binding region of aggrecan to HA. The GAG attachment region of aggrecan provides the high anionic charge density needed to bind water and conferring to cartilage its unique osmotic properties necessary to guarantee its functionality. Therefore, understanding the biochemical mechanisms leading to aggrecan cleavage might help in the development of therapeutics suitable to block or control the OA disease. Loss of cartilage integrity in arthritis is associated with impaired aggrecan integrity due to proteolytic cleavage of the protein. Aggrecanases (mainly aggrecanase-2, also named ADAMTS-5 and aggrecanase-1, also named ADAMTS-4), were recently identified as being among the key enzymes for cartilage degradation. In particular, the publications Glasson et al., 2005. Nature. 434:644-648) and Stanton et al., 2005. Nature. 434:648-652), demonstrated that ADAMTS-5 plays a fundamental role in the pathological joint changes associated with two models of OA and of RA in the mouse. Both ADAMTS-4 and -5 are glutamyl endopeptidases and cleave aggrecan at five specific sites: Glu373-Ala374 (interglobular domain-IGD), Glu1545-Gly1546, Glu1714-Gly1715, Glu1819-Ala1820, and Glu1919-Leu1920 bonds (human sequence), resulting in cartilage destruction.
Human ADAMTS-4 (FIG. 1, SEQ. ID NO: 1) and ADAMTS-5 (FIG. 1, SEQ. ID NO: 2) are multidomain metalloproteinases secreted from the cell into the extracellular space. Both enzymes have a similar domain arrangement consisting of a signal sequence (SS), a prodomain (Pro), a catalytic metalloproteinase domain (Cat), a disintegrin (Dis) domain, a thrombospondin type I (TS) domain, a cysteine-rich (CysR) domain, and a spacer (Sp) domain. In addition, ADAMTS-5 contains an extra TS domain after the spacer domain. All the above mentioned domain regions outside the catalytic domain, play significant roles in recognition and processing of natural protein substrates, are termed “exosites”.
It was demonstrated, for instance, that the Sp and CysR domains of aggrecanases contain GAG-binding motifs that modulate the affinity of the proteinases for their substrates (Kashiwagi et al., 2004. J Biol Chem. 279:10109-10119); (Gendron et al., 2007. J Biol Chem. 282:18294-18306); (Flannery, Curr. 11:614-619); (Zeng et al., 2006. Biochim Biophys Acta. 1760:517-524).
Thus, interest has been growing in the development of inhibitors for ADAMTS-4 and -5 for the treatment of OA and/or RA. Numerous metalloproteinase inhibitors have been developed, and several were clinically tested in patients with cancer (Zucker et al., 2000. Oncogene. 19:6642-6650) and rheumatoid arthritis (Milner and Cawston, 2005. Curr Drug Targets Inflamm Allergy. 4:363-375), but they failed to show efficacy and exhibited side effects such as musculoskeletal pain and mild thrombocytopenia (Zucker et al., 2000. Oncogene. 19:6642-6650). These failures are thought to be due to the lack of selectivity of the inhibitors and inhibition of biologically important off-target metalloproteinases and other effects. Selectivity is thus a prerequisite for nontoxic therapeutic inhibitors. One way to increase selectivity against specific metalloproteinases is to generate allosteric or exosite binding. Inhibitors that bind to an enzyme exosite could block interaction with natural ECM substrates and could be an attractive alternative to active site-directed inhibitors because they can be highly specific and effectively block hydrolysis only of the target substrate, thus minimizing in vivo side effects (Troeberg et al., 2008. Faseb J. 22:3515-3524).
The application WO 2011/002968 discloses an antibody capable of binding to both the catalytic domain and desintegrin domain of human ADAMTS-5. The documents WO 01/11074 and WO 00/53774 disclose an ADAMTS-5 protein and generally refer to antibody against such protein.